Anaerobic treatment method and apparatus

Abstract

Anaerobic treatment of water is performed under anaerobic conditions with a biofilm formed on a surface of a fluid non-biological carrier in a reaction vessel. Stable high-load treatment is performed by preventing the blockage of the reaction vessel caused by the flotation and adhesion of the non-biological carrier in the reaction vessel and effectively recovering the settleability of the carrier floating owing to adhering air bubbles by simple means. A reaction vessel is charged with a fluid non-biological carrier having a size in the range of 1.0 to 5.0 mm and a settling velocity in the range of 200 to 500 m/h. Part of the carrier that has floated and flowed out of the reaction vessel is fed downward through a pipe having a vertical height of 50 cm or more so as to remove air bubbles adhering to the carrier and is returned to the reaction vessel.

The invention claimed is: 
     
       1. An anaerobic treatment method, comprising: supplying water to be treated to a reaction vessel charged with a fluid non-biological carrier under anaerobic conditions to form a biofilm on a surface of the non-biological carrier, thereby treating the water to be treated,
 wherein the reaction vessel is charged with a non-biological carrier having a size in the range of 1.0 to 5.0 mm and a settling velocity in the range of 200 to 500 m/h, and 
 the carrier contained in treated water flowing out of the reaction vessel is returned to the reaction vessel after air bubbles adhering to the carrier are removed. 
 
     
     
       2. The anaerobic treatment method according to  claim 1 , wherein treated water containing the carrier flowing out of the reaction vessel is fed downward through a pipe having a vertical height of 50 cm or more so as to remove air bubbles adhering to the carrier. 
     
     
       3. The anaerobic treatment method according to  claim 1 , wherein the carrier from which the air bubbles have been removed is separated from treated water with a screen or a settling tank and is returned to the reaction vessel through a pump. 
     
     
       4. An anaerobic treatment apparatus for supplying water to be treated to a reaction vessel charged with a fluid non-biological carrier under anaerobic conditions to form a biofilm on a surface of the non-biological carrier, thereby treating the water to be treated,
 wherein the carrier charged into the reaction vessel has a size in the range of 1.0 to 5.0 mm and a settling velocity in the range of 200 to 500 m/h, and 
 the anaerobic treatment apparatus has means for removing air bubbles adhering to the carrier contained in treated water flowing out of the reaction vessel and means for returning the carrier to the reaction vessel after the air bubbles have been removed. 
 
     
     
       5. The anaerobic treatment apparatus according to  claim 4 , wherein the means for removing air bubbles adhering to the carrier is a pipe having a vertical height of 50 cm or more through which treated water containing the carrier flowing out of the reaction vessel flows downward. 
     
     
       6. The anaerobic treatment apparatus according to  claim 4 , wherein the means for returning the carrier to the reaction vessel after the air bubbles have been removed includes a screen or a settling tank for separating treated water from the carrier from which the air bubbles have been removed and a pump for returning the carrier that has passed through the screen or the settling tank to the reaction vessel. 
     
     
       7. An anaerobic treatment method, comprising: supplying water to be treated to a reaction vessel charged with a fluid non-biological carrier under anaerobic conditions to form a biofilm on a surface of the non-biological carrier, thereby treating the water to be treated,
 wherein the non-biological carrier is formed of the following foam (I) and/or (II), and the carrier has a size in the range of 1.0 to 5.0 mm and a settling velocity in the range of 200 to 500 m/h: 
 (I) a foam containing a resin component mainly composed of a polyolefin resin and a hydrophilizing agent of a cellulose powder, the resin component constituting 30% to 95% by weight of the foam, the hydrophilizing agent constituting 5% to 70% by weight of the foam, the foam having surface melt fracture, and 
 (II) a foam containing a resin component mainly composed of a polyolefin resin, a hydrophilizing agent of a cellulose powder, and an inorganic powder, the resin component constituting 30% to 95% by weight of the foam, the hydrophilizing agent constituting 4% to 69% by weight of the foam, the inorganic powder constituting 1% to 30% by weight of the foam, the foam having surface melt fracture. 
 
     
     
       8. The anaerobic treatment method according to  claim 7 , wherein the surface melt fracture of the foam has a specific surface area ratio represented by the following formula (1):
     B/A= 1.5 to 4.0  (1)
 
 wherein A denotes the apparent specific surface area of the foam, and B denotes the actual specific surface area of the foam. 
 
     
     
       9. The anaerobic treatment method according to  claim 7 , wherein the hydrophilizing agent is exposed on or protrudes from a surface of the foam. 
     
     
       10. The anaerobic treatment method according to  claim 7 , wherein the resin component has a melt flow index in the range of 5 to 25 g/10 min. 
     
     
       11. The anaerobic treatment method according to  claim 10 , wherein the resin component is polyethylene or a mixture of polyethylene and one or two or more selected from the group consisting of polypropylene, polystyrene, and ethylene-vinyl acetate copolymers. 
     
     
       12. The anaerobic treatment method according to  claim 7 , wherein the foam has an expansion ratio in the range of 2 to 10 and a specific density in the range of 0.10 to 0.80 g/ml as determined from apparent volume. 
     
     
       13. The anaerobic treatment method according to  claim 7 , wherein the reaction vessel is an upflow reaction vessel. 
     
     
       14. An anaerobic treatment apparatus for supplying water to be treated to a reaction vessel charged with a fluid non-biological carrier under anaerobic conditions to form a biofilm on a surface of the non-biological carrier, thereby treating the water to be treated,
 wherein the non-biological carrier is formed of the following foam (I) and/or (II), and the carrier has a size in the range of 1.0 to 5.0 mm and a settling velocity in the range of 200 to 500 m/h: 
 (I) a foam containing a resin component mainly composed of a polyolefin resin and a hydrophilizing agent of a cellulose powder, the resin component constituting 30% to 95% by weight of the foam, the hydrophilizing agent constituting 5% to 70% by weight of the foam, the foam having surface melt fracture, and 
 (II) a foam containing a resin component mainly composed of a polyolefin resin, a hydrophilizing agent of a cellulose powder, and an inorganic powder, the resin component constituting 30% to 95% by weight of the foam, the hydrophilizing agent constituting 4% to 69% by weight of the foam, the inorganic powder constituting 1% to 30% by weight of the foam, the foam having surface melt fracture. 
 
     
     
       15. A method for treating organic wastewater, comprising: supplying wastewater containing an organic substance to a reaction vessel containing a non-biological carrier to biologically treat the wastewater with an anaerobic microorganism adhering to the non-biological carrier, wherein at the startup of the reaction vessel the organic wastewater begins to be supplied to the reaction vessel containing the non-biological carrier and methanogen granules, the volume ratio of the non-biological carrier to the methanogen granules being in the range of 100:5 to 100:500, and the organic wastewater is continuously supplied to decompose and disperse at least some of the methanogen granules in the reaction vessel. 
     
     
       16. The method for treating organic wastewater according to  claim 15 , wherein the organic wastewater has an organic substance concentration of 2000 mg-COD Cr /L or less. 
     
     
       17. The method for treating organic wastewater according to  claim 15 , wherein the reaction vessel is a fluidized bed reaction vessel, and the organic wastewater is fed upward to the reaction vessel. 
     
     
       18. The method for treating organic wastewater according to  claim 15  wherein the reaction vessel has a sludge loading in the range of 0.8 to 3.0 kg-COD Cr /kg-VSS/day.